arXiv : Constraints from microlensing experiments on clustered primordial black holes

García-Bellido, Juan; Clesse, Sebastien

doi:10.1016/j.dark.2018.01.001

Article
Report number	CERN-TH-2017-206 ; IFT-UAM-CSIC-17-094 ; arXiv:1710.04694
Title	Constraints from microlensing experiments on clustered primordial black holes
Related title	Constraints from microlensing experiments on clustered primordial black holes
Author(s)	García-Bellido, Juan (Madrid, IFT ; CERN) ; Clesse, Sebastien (Louvain U., CP3 ; RWTH Aachen U. ; Namur U.)
Publication	2018-03
Imprint	2017-10-12
Number of pages	5
Note	6 pages, 3 figures, comments welcome
In:	Phys. Dark Univ. 19 (2018) 144-148
DOI	10.1016/j.dark.2018.01.001
Subject category	hep-th ; Particle Physics - Theory ; gr-qc ; General Relativity and Cosmology ; astro-ph.GA ; Astrophysics and Astronomy ; astro-ph.CO ; Astrophysics and Astronomy
Abstract	It has recently been proposed that massive primordial black holes (PBH) could constitute all of the dark matter, providing a novel scenario of structure formation, with early reionization and a rapid growth of the massive black holes at the center of galaxies and dark matter halos. The scenario arises from broad peaks in the primordial power spectrum that give both a spatially clustered and an extended mass distribution of PBH. The constraints from the observed microlensing events on the extended mass function have already been addressed. Here we study the impact of spatial clustering on the microlensing constraints. We find that the bounds can be relaxed significantly for relatively broad mass distributions if the number of primordial black holes within each cluster is typically above one hundred. On the other hand, even if they arise from individual black holes within the cluster, the bounds from CMB anisotropies are less stringent due to the enhanced black hole velocity in such dense clusters. This way, the window between a few and ten solar masses has opened up for PBH to comprise the totality of the dark matter.
Copyright/License	Elsevier B.V. (License: arXiv nonexclusive-distrib. 1.0)

$The individual mass distributions of the observed LIGO black holes before (blue curves) and after (red curves) merging. The sum of all individual black hole mass distributions, including the final merged ones (purple). Taking all of them into account, one obtains a weighted sum of the Adv\-LIGO black hole mass distribution, which is a lognormal with $\mu=25\,\Msun$ and $\sigma=0.5$ (green curve).$ $Synthetic microlensing constraints for an extended lognormal mass distribution of width $\sigma=0.5$, assuming PBH spatial uniformity, the x-axis representing the central mass $\mu$. The blue and orange contours correspond to the expected constraints for a {\em monochromatic} distribution ($\sigma \simeq 0$). The green and red lines are the {\em modified} constraints when taking into account the width of the PBH distribution~\cite{Carr:2017jsz}. The purple line is the overall microlensing constraint. The (light grey) curve shows the distribution for $\mu = 25 M_\odot$ and $\sigma=0.5$, excluded by microlensing if $f_{\rm PBH} = 1$ and PBH have a uniform spatial distribution. The narrow (black) distribution on the right is the equivalent distribution for the same extended-mass model but clustered PBH with $\Ncl =100$ members per cluster. It is a lognormal with $\bar\mu = 2200\,\Msun$ and $\bar\sigma=0.053$ which passes all microlensing constraints.$ $Observational constraints on PBH from a plethora of experiments (for a review see~\cite{Carr:2016drx}). We have taken into account the fact that our mass distribution is wide, which changes the constraints (grey line), for details see Ref.~\cite{Carr:2017jsz}. We have assumed PBH to be distributed as a lognormal distribution with $\mu\sim25\,\Msun$ and $\sigma\sim0.5$ (red dashed curve). The mass-equivalent clustered distribution has $\bar\mu\sim2200\,\Msun$ and $\bar\sigma\sim0.053$ (purple dot-dashed curve). Clearly the final PBH distribution passes all constraints, and at the same time constitute all of dark matter.$ Show more plots

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